The optical tweezers technology is known which is a technology for trapping, for example, a particle measuring about 1 μm and, furthermore, moving it (refer to Patent document 1, for example). According to the optical tweezers technology, a laser beam is focused with a lens and a particle that is brought close to a focusing point is trapped by optical pressure acting on it. The optical tweezers technology makes it possible to continue to trap a particle by providing a refractive index difference between the particle and what exists around it and directing the total force of optical pressure acting on the particle to the focusing point.
To trap a particle utilizing the optical tweezers technology described above, it is necessary that the particle have transmittivity (transmit the laser beam) and that the refractive index (n2) of the particle is larger than the refractive index (n1) of what exists around it (n2>n1).